_search= queries now correctly escaped, fixes #651

Queries with reserved words or characters according to the SQLite
FTS5 query language could cause errors.

Queries are now escaped like so:

    dog cat => "dog" "cat"

tests/test_api.py

@@ -947,6 +947,11 @@ def test_sortable_columns_metadata(app_client):
                 [2, "terry dog", "sara weasel", "puma"],
             ],
         ),
+        (
+            # Special keyword shouldn't break FTS query
+            "/fixtures/searchable.json?_search=AND",
+            [],
+        ),
         (
             "/fixtures/searchable.json?_search=weasel",
             [[2, "terry dog", "sara weasel", "puma"]],